On February 27 and 28 a Systems Requirements Review (SRR) of the Stratospheric Aerosol and Gas Experiment (SAGE) III was conducted at Ball Aerospace, the instrument developers facility located in Boulder, CO.
The SRR objectives were to:
This review replaces the Conceptual Design Review and is an attempt to implement the design review process identified in the new NASA Handbook on the development of space systems. The major difference between this review and the Conceptual Design Review is the emphasis that the instrument concept can meet the objectives and requirements within programmatic constraints. Major emphasis is placed on all NASA projects to stay within cost or be subject to the Agency's 15% overrun termination policy.
SAGE III is a major part of the Mission to Planet Earth's (MTPE) strategic plan. The overall objective of MTPE is to monitor changes in the environment and to provide an understanding of the Earth system that allows credible predictions of future change. SAGE III will provide data to satisfy key parts of this objective.
The Phase C/D funds to Ball Aerospace began on January 13, 1995, for a first instrument delivery date of December 1, 1997.
The SAGE III instrument is being developed to maintain the robust concept and design of the SAGE II instrument. The SAGE II worked well and was very reliable. It used solar occultation to examine the atmosphere. SAGE III operates in the same way, but it has added lunar occultation. This allows the observation of some atmospheric gases that exist only at night. It also greatly expands the global coverage. Instrumentally, the most significant fundamental design change is the replacement of single diodes, each representing a wavelength channel, with an 800-element CCD (Charge Coupled Device) linear array of detectors covering the wavelength range 290 nm to 1550 nm. Use of the linear array provides 1-nm resolved channels for measurements of multiple absorption features of a particular gaseous species and for multiple wavelength broadband extinction by aerosols, both of which greatly increase the retrieval accuracy. Ball Aerospace built the SAGE II and has a letter contract to build the new instrument.
The LaRC SAGE III Project staff presented the mission requirements. Because the instruments are flying on three different platforms (identified on page 3 in a separate article on the SAGE III Science Team meeting), different launch and flight environments will be encountered. The project design philosophy is to design a generic instrument and only make changes as required by the particular flight. The known requirements for the Russian and the Space Station (SS) flights were presented. For the SS flight, the SAGE instrument may be mounted onto an ESA developed pointing system "hexapod" for instrument pointing requirements and integrated onto an EXPRESS pallet platform that is being designed for external payload attachment to the SS. The SAGE instrument would be mounted onto the hexapod and the hexapod would be mounted onto the EXPRESS pallet. The EXPRESS pallet will be launched on the Shuttle and once in orbit will be robotically installed onto the SS. Both the hexapod and EXPRESS pallet are "new" developments and therefore create a potential risk to the program. It was recognized that interface agreements between ESA for the hexapod and SS for the EXPRESS pallet are needed as soon as possible.
The LaRC SAGE III Project staff presented the system performance requirements and allocations. The mass allocation presented was estimated based on the SAGE II instrument. It was suggested by the review team that a "bottoms up" estimate be used to ensure that these allocations are adequate. It was also suggested that a weight contingency be established and maintained by the project. The SAGE III has been defined by NASA as a Class C flight experiment.
In summary, the SRR went well in spite of the lack of a contract and the lack of complete definition of the launch and orbital environment.